Heh, perhaps we should petition to have a new computer key and symbol added to the world's way of writing maths, something like maybe a downward angled slash to mean prefix (-) :) --- On Thu, 9/17/09, Job Vranish <jvranish@gmail.com> wrote: From: Job Vranish <jvranish@gmail.com> Subject: Re: [Haskell-cafe] Re: [Haskell-beginners] map question To: "Gregory Propf" <gregorypropf@yahoo.com> Cc: "Tom Doris" <tomdoris@gmail.com>, "Haskell-Cafe" <haskell-cafe@haskell.org>, joostkremers@fastmail.fm Date: Thursday, September 17, 2009, 9:04 AM (-) happens to be the only prefix operator in haskell, it also an infix operator. so:
4 - 2 2 -3 -3
((-) 5) 3 -- note that in this case (-) is treated like any regular function so 5 is the first parameter
2
(5 - ) 3 2 (-5 ) -5 (flip (-) 5) 3 -2
It's a little wart brought about by the ambiguity in common mathematical syntax. If you play around in ghci you should get the hang of it pretty quick. - Job On Thu, Sep 17, 2009 at 11:08 AM, Gregory Propf <gregorypropf@yahoo.com> wrote: Remember that there is asymmetry between (+) and (-). The former has the commutative property and the latter does not so: (+) 3 4 = 7 and (+) 4 3 = 7 but (-) 3 4 = -1 and (-) 4 3 = 1 --- On Thu, 9/17/09, Tom Doris <tomdoris@gmail.com> wrote: From: Tom Doris <tomdoris@gmail.com> Subject: Re: [Haskell-beginners] map question To: "Joost Kremers" <joostkremers@fastmail.fm> Cc: beginners@haskell.org Date: Thursday, September 17, 2009, 6:06 AM This works: map (+ (-1)) [1,2,3,4] 2009/9/17 Joost Kremers <joostkremers@fastmail.fm> Hi all, I've just started learning Haskell and while experimenting with map a bit, I ran into something I don't understand. The following commands do what I'd expect: Prelude> map (+ 1) [1,2,3,4] [2,3,4,5] Prelude> map (* 2) [1,2,3,4] [2,4,6,8] Prelude> map (/ 2) [1,2,3,4] [0.5,1.0,1.5,2.0] Prelude> map (2 /) [1,2,3,4] [2.0,1.0,0.6666666666666666,0.5] But I can't seem to find a way to get map to substract 1 from all members of the list. The following form is the only one that works, but it doesn't give the result I'd expect: Prelude> map ((-) 1) [1,2,3,4] [0,-1,-2,-3] I know I can use an anonymous function, but I'm just trying to understand the result here... I'd appreciate any hints to help me graps this. TIA Joost -- Joost Kremers, PhD University of Frankfurt Institute for Cognitive Linguistics Grüneburgplatz 1 60629 Frankfurt am Main, Germany _______________________________________________ Beginners mailing list Beginners@haskell.org http://www.haskell.org/mailman/listinfo/beginners -----Inline Attachment Follows----- _______________________________________________ Beginners mailing list Beginners@haskell.org http://www.haskell.org/mailman/listinfo/beginners _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe